Anodizing produces thin layers of aluminum oxide on the surface of aluminum or alloys thereof. These surfaces are then made tight in the manufacturing process, usually by treating with boiling water, to close the pores of the surfaces. The aluminum or aluminum alloy surfaces treated by this method are very hard and are protected against weathering.
Such anodized aluminum or aluminum alloy surfaces frequently find practical application because of their highly protective effect and attractive appearance, especially for exterior use. For example, large-area aluminum parts with anodized surfaces often are used to cover outside walls of buildings.
Neutral cleansers are recommended for the cleaning of anodized surfaces of aluminum and its alloys since alkaline cleansers readily attack or corrode the metal surface of the aluminum.
The cleaning action of neutral cleansers without abrasives is frequently inadequate, particularly in the construction field, for the cleaning of badly soiled metal facades of aluminum or similar material. When neutral cleansers with a content of abrasives are used, the desired cleaning effect may be obtained, but this method is quite time-consuming and expensive.
Phosphoric acid esters with short chains have been suggested as acid cleanser components with little corrosive action. However, without a mechanical boost, even these types of materials only remove superficially attached soils.
Finally, acid cleansers for anodized aluminum surfaces are known from German published application (DE-AS) No. 27 21 573. These agents consist of an acid treatment solution having a pH in the range of from 0.8 to 3 and contain complex fluorine-containing compounds of boron, aluminum, silicon, titanium, or zirconium, which compounds are used either singly or as a mixture. A good cleaning effect is obtained and no measurable attack on the oxide layer is observed after a contact period lasting up to five minutes.
However, considerably longer times of contact with the cleanser during the cleaning of building facades, particularly on less accessible elements of such facades, is unavoidable. A cleaning method that allows the removal of relatively strong soiling from metal facades with less expenditure than is required for abrasive cleaning and without corrosion of the facade material upon longer contact with the cleanser thus would offer considerable advantages for practical use.